In 1877, he started the season playing for a semi-pro team in Memphis, TN, then when that team disbanded in mid-July, he agreed to terms with the St. Paul Red Caps of the League Alliance, a loose association of professional teams from around the country, for $75 per month and a train ticket to Minnesota. However, later that month, he jumped the team when they were playing in Manchester, NH and joined the local squad. It was one of the first publicized cases of "contract-jumping". The Red Caps complained to other organized leagues at the time, including at the National League's winter meetings, and St. Paul won the day over Walker's objection that he had never had never signed an actual contract. As a result, Walker was suspended for a year.

When he returned, Walker was one of the better hitters on the 1879Buffalo Bisons, and although he hit .230 and .239 in 1880 and 1882, had batting, on-base, and slugging averages better than his teams' averages in those years. In a dubious accomplishment on June 20, 1879, he became the first major leaguer to strike out five times in a game. In 1882, he led the American Association in home runs. In 1884, he had the highest batting, on-base, and slugging averages on his team, the Brooklyn Atlantics.

He played roughly equal numbers of games at first base and in center field during his major league career. He originally signed with St. Paul for the 1877 season, but then joined Manchester, who dropped him on September 2. On December 5, Walker's expulsion was handed down for "contract jumping."

He died at age 35 in Brooklyn, the town in which he had been born and the town in which he had played in 1875 and 1884.